Microscopic Lumbar Diskectomy techniques were developed and championed by Dr. Robert Williams in the late 1970's and by Dr. John McCullough in the late 1980's and 1990's. For the first time since the advent of Lumbar Disc Surgery by Mixter and Barr in 1934 a method was introduced allowing Lumbar Disc Surgery to be performed through a small incision safely resulting in faster patient recovery and converting a two to five hospital stay procedure virtually to an outpatient procedure.
The special retractors developed by Drs. Williams and McCullough however were often difficult to maintain in optimum position and relied on the interspinous and supraspinatus ligaments for a counter fixation point severely stretching these structures. This stretching along with the effects of partial facectomy, diskectomy, removal of the ligamentum flavum and posterior longitudinal ligament contributed to the development of Post Diskectomy Instability. Taylor retractors were also used but were cumbersome, required larger incisions and often injured the facet joints.
A second generation MIS retractor system was introduced by Dr. William Foley in 1997, and which was a tubular system mated to an endoscope which he labeled a Minimal Endoscopic Diskectomy (MED) system. It featured sequentially dilating the Lumbar Paraspinous Muscles allowing a working channel to be advanced down to the level of operation through which nerve root decompression and Diskectomy Surgery could be performed. Minor changes were made with the second generation METRx system. However, there were several disadvantages to the MED and METRx systems.
In the MED and METRx systems, the cylindrical working channel considerably restricted visualization and passage of instruments. It also compromised the “angle of approach” necessary for safe usage of the operating instruments. This problem was proportionately aggravated with the long length of the tube. This compromised visualization contributed to the following problems, including nerve injury, dural tear, missed disc fragments, inadequate decompression of the lateral recess, increased epidural bleeding, difficulty controlling epidural bleeding, inadequate visualization of the neuroforamen, and inadequate decompression of neuroforamen.
The repetitive introduction of successively larger dilators caused skin abrasion with the potential for carrying superficial skin organisms down to the deeper tissue layers hypothetically increasing the risk of infection. The learning curve for operating in a two dimension endoscopic field proved to be arduous and contributed to the above complications.
The attempted use of the METRx system for more complex procedures such as fusion was further hazardous by inherent limitations. Endius in September of 2000 then introduced a similar device which differed by having an expandable foot piece to allow greater coverage of the operative field. However, the enlarged foot piece was unwieldy and difficult to seat properly. Exposure of the angle of approach was also limited by having to operate through a proximal cylindrical tube with its limitations as described before. In comparison to the METRx system the working area was improved but access was again restricted by the smaller proximal cylinder.
Both systems offered endoscopic capability but many spine surgeons chose to use an operating microscope or loupes to maintain 3-Dimensional visualization rather than the depth impaired 2-Dimensional endoscopic presentation. Keeping debris off of the endoscopic lens has also proved to be a troubling challenge.
More recently, the third generation of MIS Retractors have been designed for general and spine surgery (Nuvasive (Pimenta et al)), Quadrant (Branch et al), Depuy-Pipeline (Raymond et al). There have also been modifications of older devices offering to enter the arena of MIS Spine Surgery (Koros). The plethora of proposed surgical retraction devices and methods have led to a confusion of meaning of the “MIS Spine Surgical Technique.” Surgical incisions of up to five inches in length have been described for MIS Surgery. Usage of the term “MIS Surgery” as applied to spine surgery, appears to have evolved to mean a surgical incision less than the traditional one or two levels above and below the surgical field of interest. However, the combined length of two incisions (right and left) often is longer than the single midline incision. The true advantage of MIS Surgery over the traditional technique is the specificity of exposure such that only the required amount of retraction of soft tissue is used to safely accomplish the specific surgical procedure.
Ideally, there are certain prerequisites for a MIS spine retractor that should be fulfilled in order to accomplish the objective that only the required amount of retraction of soft tissue is used:                1. The retractor must provide sufficient direct visualization of the neural elements, related blood vessels, and bony landmarks to accomplish safe spine surgery.        2. The retractor should require the least amount of resection of adjacent tissue muscle, fascia, bone, and joints to accomplish the task.        3. The retractor should be self-retaining instead of hand-held (Ritland).        4. Deployment of the surgical retractor should be able to be prompt and precise in location.        5. The retractor should be easy to adjust for length, width, and angle of exposure.        6. The retractor support, such as a frame, must have the capability to lie flat to the surface contour of the body so that the attached retractor blades could be as short as possible.        7. The retractor support, such as a frame and blades must be stable once optimum surgical exposure is obtained.        8. There should be a minimum of “fiddle factor” so the surgeons attention can remain focused on the operation and not distracted by the complexity of using the retractor.        9. The retractor must be “strong enough” in design not to flex and lose exposure.        10. Particularly for surgery of the posterior lumbar spine, the retractor must be designed to counter the powerful paraspinal muscle resistance without using large incremental changes (e.g. widely spaced ratcheted gap).        11. With longer exposure length, there must be an efficient means to retract muscle that encroach between the retractor blades.        12. The need for ancillary equipment such as light source attachments, etc., are self evident.        
Currently available surgical retractor systems fail to fulfill all of the above requirements. Consequently there is a severe need for structures and procedures to meet such requirement.
Due to the spine surgeon's desire to utilize the advantages of MIS Surgery to evermore complex procedures, the MIS Surgical Retractors have evolved to attempt accommodate this need. For example. the Danek MED Tube evolve to the X-Tube and then to the Quadrant system (U.S. Pat. No. 6,945,933 to Branch et. al, Dewey et al). Still other retractor inventions have come to market including the three-bladed, Nuvasive design for the lateral approach to the Lumbar Interbody Space, the Depuy “pipeline” retractor, a highly complex four-bladed retractor system with a curved ratchet arm, the Stryker Luxor. None of the above retractor Systems incorporate the full complement of prerequisites listed above.
The Branch, et al. System's new retractor creates a “working channel” with insertion of sequentially larger dilating tubes. This method of introduction into the body while acceptable for use with an enclosed tube encounters problems when the newer systems with retractor blades which can be opened apart are utilized. With the serial dilation techniques the strong fascia and paraspinal muscles have remained intact, and therefore a monumental battle develops between the separating blades and the intact muscle and fascia resisting the expansion. This necessarily results in tearing and shredding of the muscle as the blades are forced apart.
This is acknowledged by Branch et al '933 reference at page 10, paragraph 2. “In use, the resistance to retraction provided by the tissue may prevent distal ends from separating as far as proximal ends.” In the Branch/Dewey system this is always the case when spine surgery is attempted at more than one level. Since the muscles have retained their strong attachment to the bone, forcing of the retractor blades apart necessarily requires ripping and shredding of the muscles and associated blood vessels and nerves.
The Quadrant System retractor blade separation is also based on a straight ratchet bar and therefore cannot accommodate for Lumbar lordosis which is often forty degrees at the lumbosacral junction. This requires retractor blades to be longer as the frame tends to “ride up from the surface of the skin” due to the curvature of the surface anatomy.
The retraction blades of the Quadrant system are also cantilevered a considerable distance from their attachment point on the ratchet bar creating unwanted movement, stress, and loss of muscle retraction compromising exposure. Applying a force from such a distance tends to (1) lose control of soft tissue retraction and therefore compromises the “working channel”, (2) loads stress into bending and compression moments of a mechanical apparatus, and (3) having the mechanical apparatus block the surgical area while it is being employed. Therefore, the Quadrant system's retractor blades location at a considerable distance from its base attachment point on its ratchet bar creates a long lever arm moment which lends instability to the retractor blades. The Branch reference also shows a curved frame but this cannot adjust to different lordotic angles of the patient's posterior lumbar area.
The Pipeline retractor, while adequate for one level posterior lateral fusion procedure, has the deficiencies as described in the Quadrant System because of the serial dilation introduction method and suffers from negative effects of its extreme complexity. Raymond attempts to address the need to accommodate for lower lumbar lordosis by using a curved ratchet frame, but their fixed curvature cannot adjust to different lordotic angles. In addition, the Pipeline retractor has proven extremely difficult to spread the retractor blades up an inclined slope along the arc of the ratchet arms against the strong resistance of the muscle and fascia even using a separate spreader device. The Pipeline device also has proven to be so complex that it is very difficult and time consuming to set up, operate, and learn to use.
The Nuvasive Retractor (Pimenta) is suitable for the lateral approach to the L2, L3 and L4 levels for which the retractor was designed. The deficiencies of a three bladed retractor like Nuvasive's become apparent when used for other procedures such as a posterolateral lumbar fusion. If the Nuvasive retractor is deployed such that the middle blade is lateral, then visualization of the spinal canal can be difficult. If the Nuvasive middle blade is placed medial, there is significant muscle encroachment as the blades are spread apart.
Another reference, Cocchia's U.S. Pat. No. 6,224,545 has a number of shortcomings, including (1) a surgical frame having no structure to allow flexion and extension, (2) retractor blades which are rotated with an awkward force plate device, and (3) the knobs used to control movement of the device are difficult to use due to the proximity on the patient's skin and inability to apply adequate torque.
Further, Cocchia's device requires a completely open slot in the arms of the main frame, along which is run a cylindrical guide bar. The Cocchia device also requires two additional “traveling rods” on the thread assembly cross piece to keep the moving parts from binding. Coccia's design also has an exposed, open end of the screw device which can tear surgical gloves and tissues predisposing to infection.
Coccia's use of a force plate method to provoke angulation of the retractor blade, also lacks the control to return to neutral from outward deflection. The force control of Coccia's device furthermore does not contemplate force movement to an inwardly angled position. As a result, Coccia's device is impractical for advanced retraction needs.
As discussed above, it is advantageous to have a retractor frame that can adjust to the body surface where the surgery is being performed. Historically, several retractors for general purposes have had a hinge, usually on the handles of the retractor (Beckman) or on the frame (Koros, Watanabe) to lower a portion of the retractor out of the way of the surgeon's hands. The hinges did not serve the purpose of contouring the device to the surface of the body.
The axis of rotation of these hinge devices is therefor cephalo-caudal or in the longitudinal axis of the body. Turning these retractors 90° would be counter to the general intended use of these retractors. Furthermore, the retractor hinges were “free moving” and did not have control devices.
The Bookwalter retractor did have two hinges connecting two halves of a circular or elliptical frame with an angular control device. The angulation was controlled by interdigitating rings which were locked into position with thumbscrews. This allowed flexion and extension of the basic hoop frame, but required loosening of the thumbscrews, disengaging the ratchets, adjusting to a new position, reengaging the ratchets and re-tightening the screws. This arduous process is allowable for abdominal surgery but is unacceptable for MIS spin surgery.
In order to attain ideal exposure at the surgical work area, it is also important to have customized retractor tips. The value of “docking” of the distal end of the retractor has been described for closed tube MIS retractor systems by Michelson (U.S. Pat. No. 6,080,155) and Simonson (U.S. Pat. No. 7,008,431). These concepts have not been able to be employed in higher level retractor systems.